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[Display omitted] • The ultrathin Ni-phyllosilicate was successfully synthesized by ball milling method. • H 2 O 2 played a crucial role of pore-forming reagent to create defects in Ni-phyllosilicate. • Nickel acetylacetonate was the optimal nickel salt precursor to form Ni-phyllosilicate. • Metal utilization rate was significantly improved owing to the ultrathin defect-rich structure. • The optimum catalyst exhibited enhanced low-temperature activity for CO 2 methanation. To address the problems of low metal utilization rate and poor low-temperature activity of the nickel phyllosilicate catalysts for CO 2 methanation, this work prepared ultrathin defect-rich Ni-phyllosilicate through ball milling method in the presence of H 2 O 2 modifier, which simultaneously created active sites with more quantity and higher quality. The instantaneous temperature and high pressure derived from the collision and friction of grinding balls provided driving force for the Ni-phyllosilicate synthesis, and the shear force destroyed the interlayer forces to construct the ultrathin layers. H 2 O 2 molecule could insert the layers and dissociate to O 2 bubbles, whose cavitation effect created holes and defects in the nickel phyllosilicate nanosheets and SiO 2 spheres. H 2 O 2 amount was crucial for the defect construction and the optimum Ni-AA-1H catalyst possessed the ultrathin nanosheet of 0.68 nm and high Ni dispersion of 15.6 %, whose TOF CO2 reached 3.76 × 10−2 s−1 at 160 °C. The in-situ DRIFTS results confirmed the enhanced low-temperature activity and the HCOO− reaction pathway over Ni-AA-1H for CO 2 methanation. Nickel precursor effect was also investigated, and nickel acetylacetonate was determined as the optimal one compared with nickel acetate and nickel chloride, owing to the high steric effect of CH 3 COCHCOCH 3 − group and strong basicity environment during ball milling process. [ABSTRACT FROM AUTHOR]

[Display omitted] • Dynamic hydrothermal method could accelerate the Ni-phyllosilicate synthesis. • Glycerol modification significantly reduced the thickness of Ni-phyllosilicate nanosheets. • Synergistic effect of stirring and viscous solvent led to enhanced activity for CO 2 methanation. • Viscous solvent-assisted dynamic hydrothermal method was competitive to synthesize Ni-phyllosilicate. To address the shortcomings of poor convection and product agglomeration of the static hydrothermal method, the dynamic hydrothermal method together with the viscous solvent-assisted dynamic hydrothermal method were proposed to synthesize Ni-phyllosilicate in this work. Stirring seemed to be powerful to accelerate the synthesis with significant increase of Ni content from 11.80 wt% (static synthesis) to 23.13 wt% (dynamic synthesis). The further modification of glycerol increased the shearing force to exfoliate the Ni-phyllosilicate nanosheets during dynamic synthesis, whose thickness could reach 1.17 nm with improved metal utilization ratio after reduction. As a result, the activity of CO 2 methanation was enhanced with large TOF CO2 of 3.5 × 10−2 s−1 and small E a of 65.13 kJ·mol−1. In situ DRIFTS analysis confirmed the existence of high actively intermediate of m -HCOO− and *CO, which could be further hydrogenated into CH x species. In short, the synergistic effect of dynamic stirring and glycerol modification drove the enhancement of catalytic activity, and also provided the possibility of large-scale production of Ni-phyllosilicate using hydrothermal method. [ABSTRACT FROM AUTHOR]

This work reported an efficient one-pot hydrothermal method for adding promoter to nickel phyllosilicate. The nickel‑samarium bimetallic phyllosilicate (NiSm-Ps) was formed during the one-pot synthesis. The characterization results showed that the Sm species over the uncalcined NiSm-Ps catalyst existed in the form of Sm 2 Si 2 O 7 , and it was converted to be Sm 2 O 3 after calcination with high dispersion, and in the form of Sm 2 O x after reduction. On the contrary, for the post-impregnated Sm-doped nickel phyllosilicate catalyst (Ni-Ps/Sm-Im), the Sm species variation was from Sm 2 O 3 to Sm 2 O x , which was significantly different from that of NiSm-Ps. As a result, the NiSm-Ps catalyst showed a high Ni dispersion (13.9%), small particle size (4.0 nm) and large concentration of surface oxygen vacancies as well as strong H 2 and CO 2 activation properties. Consequently, the NiSm-Ps catalyst achieved a high CO 2 conversion of 80.1% at 400 °C and large TOF CO2 of 4.08 × 10−3 at 220 °C. Additionally, NiSm-Ps exhibited excellent long-term stability and anti-sintering property. In short, the formation of Sm 2 Si 2 O 7 was very crucial for the Ni-Sm/SiO 2 catalyst and could further improve the promotion effect of Sm species for CO 2 methanation. [Display omitted] • The Ni Sm bimetallic phyllosilicate catalyst was synthesized by a one-pot strategy. • Sm 2 Si 2 O 7 was the important intermediate product of the one-pot synthesized catalyst. • Sm 2 O 3 rather than Sm 2 Si 2 O 7 was observed on the post-impregnated catalyst. • The occurrence of Sm 2 Si 2 O 7 led to the more significant promotion effect for CO 2 methanation. [ABSTRACT FROM AUTHOR]

Addressing the problems of easy collapse, Ni sintering and low catalytic activity over the nanotubular nickel phyllosilicate catalyst, the Mg species was doped via a simple hydrothermal method to construct the nanotubular Ni-Mg bimetallic phyllosilicate solid solution. The high thermal stability, nonreducible property and strong basicity of magnesium species led to the enhancement of anti-collapse, Ni-sintering resistance and basicity. As a result, the fine Ni particles and enhanced H 2 and CO 2 chemisorption and activation properties resulted in boosting the catalytic activity of both CO 2 methanation and CH 4 -CO 2 reforming reactions. The Ni/Mg ratios and the reduction temperatures were detailed optimized, and the 600oC-reduced Ni 8 Mg 2 -NT catalyst with the Ni/Mg ratio of 8:2 was the optimal, which also exhibited high long-term stability. In short, the formed Ni-Mg-phyllosilicate solid solution structure and the special interactions of different species brought about high catalytic performance of the nanotubular Ni-Mg phyllosilicate catalyst. [Display omitted] • The nanotubular Ni-Mg bimetallic phyllosilicate solid solution was synthesized. • Nanotubular Ni-Mg phyllosilicate obtained high anti-collapse and Ni-sintering resistance properties. • The Ni/Mg ratio of 8:2 and the reduction temperature of 600 oC were the optimum. • This catalyst was versatile for both CO 2 methanation and CH 4 -CO 2 reforming reactions. [ABSTRACT FROM AUTHOR]